Impact wrench



I Oct. 29, 1940. C. E, F11-QH 2,219,865

IMPACT WRENCH Filed oct. 14, 195s 2 sheets-sheer 1 @wg/Mam ATTORNEY Oct. 29, 1940. c. E. FITCH 2,219,865

IMPACT WRENCH Filed Oct. 14, 1958 2 Sheets-Sheet 2 a-mal ramal oct. 29,1940@ y n rrsc'r wiuiucirV 1 cunard n. nien. Gennaio, oma'mimar 'to omcago Pneumatic Ilool Company, New York, N. Y., a corporation of New Jerte! Application (lotobei' 14, 1938, Serial No. 234,884

This invention relates to clutch mechanism having particular application to impact wrenches for tightening and loosening nuts. bolts and the like with a rotational hammer action.

An object 'of the invention is the delivery of Y 15 A further object is to preventraccidental engagement and scoring of the end faces of the Yclutch teeth as theypass each other during the interval between impacts. Y

In accordance with a feature ofthe invention, the rotatable hammer, or driving clutch element, is moved into engagement with vthe `anvil by means of centrifugal weights. The weights are adapted to exert a gradually increasing axial component of pressure on the hammer as it moves toward the anvil, and vice versa. The weights are arranged to revolve with the spindle at a substantially constant speed, accumulating and releasing kinetic energy as the radius of gyration of the weights lengthens and shortens, respectively. The accumulation takes place while the hammer moves toward the anvil, and the releasing or redelivery of energy from the weights to the driving spindle occurs as the hammer moves away from the anvil. In prior constructions, employing a torsion or compression spring for storing potential energy, accumulation occurs .while the hammer moves away from the anvil and the stored energy is delivered to the hammer during its opposite movement. The advantage of the present invention -is that the kinetic energy is accumulated at a time when 'the driving spindle is under va relatively light load and is transmitted back to the spindle when the load on the latter is at a maximum.

A Other objects and features ofthe invention Y 1o claims.' (ci. 1oz-sas) positions of the parts when the driven member is under load. and at the instant that the hammer is released from driving engagement with the anvil, the rotary displacement of the centrifugal weights away from their Fig.v l position not being shown in order more clearly to illustrate their radial displacement;

Figs. 3 and 4 are cross sections as indicated by the arrows 3 and 4 respectively in Fig. 1; Y

Fig. 5 is an elevational view ofthe lower end 10 of the driving spindle and associated ball, the relative position of the hammer b elng shown in. brokenlines; n

Fig. 6 is'a longitudinal section ofthe hammer looking in the/same direction as in Fig. l; 15

Fig. 7 is a longitudinal section of the hammer, turned 90 away from the Fig. 6 position, as indicatedby the arrows 1 in Figs. 6 and 8;

Fig'. 8is a bottom plan view of the hammer illustrating also the associated balls; 20

Fig. 9 is a development of the lower end of th driving spindle, certain surfaces of thehammer being shown in broken lines, the. balls being shown in full lines, the. position of the parts corresponding to Fig. l; and 25 Fig. 10 is a developmentv similar to Fig. 9, the position of theparts corresponding to Fig. 2.v

The essential parts of the impact clutch are inclosed in a housing I2 secured by bolts I3 to a transfer plate It and motor casing (not shown). 30 The transfer plate supports a bearing I5 for a drive shaft i6, which is held against axial movement. A driving spindle Il has a cket I8 at its upper or rear end'which receives the drive shaft.

The forward part of the spindle has a recess I9 35 into which fits a cylindrical projection 20 on an anvil member 2 I. The anvil is seated, for rotary movement. in a bushing 22 secured to the bushing I2. The anvil 2| and drive shaft I6 cooperate to secure the spindle I'II against endwise and a lateral movements. The front end of the anvil is adapted to be rigidly connected to a wrench socketl23.

'I'he spindle I'I drives a rotary hammer 25 which has a'bore 26 fitting the spindle. hammer has a greater mass and moment of in'- ertia than the anvil. The front end of the hannmer is providedI with a plurality of circumferentially spaced jaws or teeth 21 adapted to move into and out of driving 'engagement with jaws 28 integral with and projecting rearwardly 'from the anvil'Zi. Preferably, there are two jaws on the hammer and anvil and each of the driving or i, impact surfaces thereof lies in a plane passing The 45 through-the axis of rotation, as shown in Figs. 4, 7 and 8.

The driving connection between the spindle I1 and hammer 25 comprises a pair of balls 38. 5 The exterior surface of the spindle is provided with two pairs of cam grooves, each pair being associated with one of the balls and comprising a right-hand spiral groove SIR and a left hand ,spiral groov 3IL. As shown in Figs. 5 and 9, the righ d left hand spirals communicate wtih each other at their lowerrends, at which point `they receive thev associated ball 30 when the clutch is in its normal or no-load con/dition. Complementary pairs of right and left hand spiral shoulders 32B and 32L respectively are formed at the rear end of a bore 33 in the hammer 25. A counterbore 34 facilitates `entrance of the balls 30 intothe spiral grooves 3IR and 3IL when the parts arev assembled. The balls, spiral shoulders and spiral grooves cooperate to resolve the driving force of the spindle into a rotary component for driving the hammer 25 and an axial component tending to pull the hammer teeth 21 out of driving engagement with the anvil teeth 28. The present invention provides a novel means for resisting the axial component of force on the hammer and of moving the hammer into re-engagement with the anvil. rI vvo pairs of ears 35 are secured integrally, or otherwise, to the spindle I1 and they support pintles 36 on parallel axes.A Each pintle provides a pivotal support for a heavy centrifugal weight 38, the weights being of equal mass and positioned on opposite sides of the spindle to prevent unbalancing forces. 'I'he weights have forwardly extending projec` tions 39 abutting against a plate 40, which is arranged to exert axial pressure against the hammer 25 through a ball bearing arrangement 40 4I. The centers of gravity of the weights are to the rear of the pintles.

In operation, the shaft I6 drives the spindle I1 at a substantially constant speed. Assuming that the wrench socket 23 offers no substantial 45 resistance to rotary movement, the parts assume the position shown in-Fig. 1 in which the hammer 25 is held in engagement with the anvil by the centrifugal force of the weights 38, and the balls 30 are at or near the lower ends of the 50 helical cam grooves SIR. As the resistance to rotation increases, the axial component of the force transmitted through the balls of the hammer correspondingly increases. As long as this axial component is less than the forward pres- 55 sure exerted against the hammer by the centrifugal Weights, the hammer teeth 21 remain in driving engagement wtih the anvil teeth 28 and r the hammer and anvil rotate in unison. When the nut or bolt (not shown) being driven by the socket 23 becomes seated, the resistance of the anvil 2| to further rotation increases abruptly and the spindle I1 continues to turn while the hammer is substantially locked against further rotary movement. The spindle moves relative to the hammer from the position shown in Figs. 1 and 9 to the position shown in Figs. 2 and 10 causing the hammer to be lifted out of engagement with the anvil, under the camming action of the helical grooves 3 IR, balls 30 and spiral shoulders 32B.. As the hammer 25 moves rearwardly,the centrifugal weights 38 are retracted or pushed towardl the center of rotation as will be seen by a comparison between Figs. 1 and 2. Upon disestablishment of the driving connection .75 between the teeth 21 and 28, the hammer is rein cooperation with the helical cam andl ball arrangement.

'I'he present invention compares favorably with prior impact wrenches employing a compression spring for accumulating energy while the hammer moves rearward and accelerating thehammer during its forward movement by virtue of such stored energy. In such prior devices, the axial pressure on the hammer by the spring accumulator increases sharply as the hammer moves away from the anvil. In the illustrative em- -bodiment of the present invention, the axial pressure on the hammer does not vary through such wide limits and decreases as the hammer moves rearward. An advantage of minimizing the axial pressure when the hammer is in the Fig. 2 position is that it prevents scoring of the end faces of the clutch teeth 21 and 28 as they pass over each other.

Another advantage of .the present invention is that it delivers a powerful blow to the anvil with relatively little shock on the continuously rotating spindle I1 and the gears (not shown) through which the spindle is driven. Neither the hammer nor the weights 38 accumulate energy while the hammer is moving away from the anvil. The centrifugal weights 38 upon being retracted, shorten their radius of gyration, thereby releasing energy to the spindle while the clutch teeth are in engagement and the hammer moves rearward. The shock transmitted to the spindle I1 through the balls at the instant of impact, which necessarily checks the speed of the spindle at that time, is partly oiset by the fact that the decrease in the radius of gyration of the weights 38- tends to augment the speed of the spindle.

In short the invention minimizes fluctuations in the torque delivered by the spindle while the hammer is delivering powerful impacts to the anvil.

The cam driving connection and the clutch teeth are symmetrically arranged whereby the operation is substantially the same for either direction of rotation of the spindle l1. When the wrench is operated to loosen a nut o r bolt, the balls ride between the cam grooves 3IL and camshoulders 32L, instead of 3IR and 32R as hereinbefore described.

What is claimed is:

1. A clutch mechanism comprising a continuously rotatable spindle, a clutch driving memlber, a clutch driven member, said clutch members having separable spaced teeth adapted to retard rotation of the driving member when the driven member encounters resistance and while the driving spindle continues to rotate, said teeth being engageable and disengageable upon movement of one member relative to the other in an axial direction, disengaging means constantly urging one of .the clutch members axially toward a position in which the clutch teeth disengage and eective to interrupt the driving connection between such clutch members when the resistance to rotation becomes excessive, and means including centrifugal weights for resisting separation of the clutch members and for automatically moving them ardally into re-engagement following separation.

2. An impact clutch comprising a driving spindle, coaxial. driving and driven clutchmembers having complementary engageable teeth, a driving connection between the spindle and the driv- 15 and for moving them into re-engagement, said centrifugal means comprising one or more weights supported for pivotal movement toward and away from the driving spindle,*said weight having an abutment positioned to move the clutch driving member axially toward re-engaging position as .the weight moves away from the spindle.

3. An impact clutch comprisinga driving spindle, an anvil adapted to be held against axial movement relative to the spindle,` a hammer, said spindle, hammer and anvil being coaxially rotatable, said hammer and anvil having complementary teeth adapted to establish a continuous driving engagement between the hammer and anvil under certain conditions of operation and to separate automatically under other operating conditions, said anvil being adapted to encounter a variable torque resistance, means responsive to an increase in such torque resistance to eifect the automatic separation aforesaid, a driving connection between said spindle and hammer permitting limited axial movement of the hammer, and means for moving the hammer automatically into re-engagement with the anvil following sep- 40 aration, said means comprising a plurality of centrifugal weights pivotally mounted relative to the spindle, each weight having an abutment positioned for moving the hammer .toward the anvil as the weight moves away from the axis of the 45 spindle.

4. An impact clutch comprising a continuously rotatable spindle, a rotatable impact vhammer driven by said spindle and supported thereon for limited axial movement, a'rotatable anvil held 50 against axial movement relative to the spindle, said hammer and anvil being coaxial and having complementary clutch teeth operative to elect a continuous drive between the hammer and anvil when the resistance to rotation of the anvil is low, means effective when the anvil meets with relatively high resistance to move the hammer axially .to declutched position, and means for exerting an axial pressure on the hammer `tending to resist separation from the anvil and to 60 move the hammer into re-engagement following such separation, said axial pressure being greater when the clutch teeth re-engage than when the clutch teeth are out of engagement, said pressure exerting means comprising one or more weights,

65 each pivotally4 mounted to swing away from Athe axis of the spindle in response to centrifugal force, the pivot for the weight being driven by the spindle and revolving therewith. l

5. An impact clutch comprising a rotatable 70 anvil, a' rotatable impact hammer for driving said anvil, complementary engageable clutch teeth carried by the hammer and anvil, said teeth being separable by axial movement of the hammer away from the anvil in response to a pre- 75 determined resistance to, rotation, a continuously the clutch driven member, said driving connecrotatable spindle.` driving connections between said'spindle and hammer including complementary cam elements, and means for automatically moving the hammer toward re-engagement withthe anvil following separation, said means cooperating'with the cam elements for causing the hammer to rotate ata greaterspeed than the spindle as the hammer approaches the re-enga'ging position, said means exerting-a gradually lncreasing axial pressure on the hammer as it moves toward the anvil. said means comprising weights mounted on pivots for swinging movement away from the axis of the spindle in response to centrifugal force and comprising driving connections for causing'the pivots to be revolved.

6. An impact ciu-tch comprising a continuously rotatable spindle, an anvil, a rotatable hammer.

complementary engageable and disengageablel clutch teeth carried by said hammer. and anvil,

driving connections between said spindle and l hammer comprising complementary cam elements, and centrifugal means for moving .the

hammer toward the anvil subsequent to the disengagement aforesaid and cooperating with said cam elements to accelerate the hammer as the latter moves toward re-engagement with the anvil, said centrifugal means comprising weights constrained to revolve in unison with the spindle but mounted for independent movement toward and away from the spindle axis.

7. In an impact clutch, the combination of a rotatable hammer, a rotatable anvil, driving clutch means between said hammer and anvil capable of release 'to enable relative rotation therebetween, cam means separate from said clutch means for effecting a relative releasing movement of said clutch means upon the imposition of an increased resistance to rotary movement of the hammer, centrifugal means for -resisting separation of such clutch means, said centrifugal means cooperating with the cam means -to assist in the acceleration of the hammer prior to the re-engagement aforesaid, said centrifugal lmeans comprising weights constrained to revolve in unison with the spindle but mounted for independent movement toward and away from the spindle axis.

8. An impact clutch comprising a hammer rotatable in both directions, an anvil coaxially rotatable therewith, the moment of inertia of said hammer being greater than that of the anvil, said hammer and anvil having complementary clutch teeth periodically releasable and re-engageable with a hammer action in response to relative axial movement between the hammer and anvil, driving means for said hammer, and in' ertia.` means rotatable in unison with said. driving for releasing such accumulated energy while the clutch teeth are in engagement, said inertia means comprising weights driven by the spindle in unison therewith andmounted for movement away from the spindle axis in response to centrifugal force.

9. An impact clutch comprising a driving spindle, an anvil adapted to be held against axial movement relative to the spindle, a hammer, said spindle, hammer and anvil being coaxially rotatable, said hammer and anvil having complementary teeth adaptedto establish a continuous driving engagement between the hammer and anvil under certain conditions of operation and to separateautomatically under other operating conditions. a.drlving connection between said spindle and hammer permitting limited -axial movement of the hammer, and means for moving the hammer automatically into re-engagement with the anvil following separation. said means comprising a plurality oi' centrifugal weights pivotally mounted relative to the spindle, each weight having an abutment positioned for movement in a direction generally parallel to the spindle axis and toward the hammer when the ra-` dius'of gyratlon oi' the weight is lengthening, and

an anti-friction thrust bearing interposed between said .abutments and the hammer, said A thrustbearing transmitting axial movement from the hammer to the weight abutments and vice versa.

10. A rotary impact tool comprising a continuously rotatable spindle: a rotatable anvil; an intermediate driving member arranged to cause delivery oi rotational hammer blows to the anvil andes ma wenn! being subjected um: ma r axially relative to the driving spindle to'ooperate with the cam means in the transmission oi torque therebetween, characterized in that said pressure means comprises a plurality oi' centrifugal weights each being-arrangedto swing about a -plvot carried by the spindle. the axis of the pivot lying in 'a plane perpendicular to theaxisoi rotation o! the spindle. l CLIFFORD E. FITCH. 

